Air filter



FIG. 1 is a rear, left side perspective view of an air filter showing my new design;

FIG. 2 is a rear plan view thereof;

FIG. 3 is a bottom elevational view thereof;

FIG. 4 is a top elevational view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a left side elevational view thereof; and,

FIG. 7 is a front plan view thereof.

The broken line representations of items in FIGS. 1-7, are for purposes of illustration only, and form no part of the claimed design. 

The ornamental design for an air filter, as shown and described. 